Background Images in the Right Orthographic Viewport Disproportionate to the Other Views
The way I deal with this is to take the three views of the object, and normalize them to the same size. Lets suppose I have the dimensions of the images of item are that the top view is 1000 pixels long by 800 pixels wide, the dimensions of the front view are 1000 pixels long by 1200 pixels tall, and the dimensions of the end view are 800 pixels wide x 1200 pixels tall. In Photoshop (R) [NB: for the record, I don't use photoshop, and do this in GIMP, but it is beyond the realm of my imagination that you can't do the same thing in photoshop] I create a canvas using the maximum of the dimensions of all three, plus a border, so I'd create a base image size (in GIMP, a "canvas") measuring 1100 x 1300 pixels. I'd make three copies of this image, and into one I'd place (so that the center of the desired part of the image is at the center of the canvas) the top view, in a second I'd place the front view, and in the third, I'd place the end view. The amount of border around the three images will vary, but the parts of the Blender image in each viewport should be both the same perceived size, and the same actual size. 

I don't usually "waste" the borders around the images, either. Using the image processing software, I'll usually edit into the borders of the background images things like scales and useful dimensions not already provided, or readily apparent, in the drawing.